Conventionally, a predetermined number of packaging containers which have been discharged from a filling machine after being filled with contents are stacked in a packing pattern, and are wrapped by a heat-shrinkable film such as polyethylene film.
The film formed in an elongated shape is rolled and is set on a payoff machine as a film roll. The film supplied from the payoff machine is continuously fed to a shrink packaging machine. The film is cut in the shrink packaging machine when a predetermined amount is used for packaging.
When a film roll is used up during a continuous packaging operation, a new film roll (hereinafter referred to as a "new roll") is set on the payoff machine, and film is taken out from the new roll. Since the wrapping of packaging containers is continuously performed at the shrink packaging machine, the tail end of a previously used film roll (hereinafter referred to as an "old roll") is joined with the leading end of the new roll, With this joining operation, film can be continuously supplied to the shrink packaging machine.
FIG. 1 is an illustration showing a conventional film joining apparatus in a state before joining films. FIG. 2 is an illustration showing the conventional film joining apparatus in a state after joining the films.
In these drawings, numeral 11 denotes an old roll, numeral 12 denotes an old film which is taken out from the old roll 11 by an unillustrated payoff machine, numeral 14 denotes a new roll, numeral 15 denotes a new film which is taken out from the new roll 14 by an unillustrated payoff machine. While the old film 12 is taken out from the old roll 11, the new roll 14 is set on the payoff machine, as shown in FIG. 1. After that, the leading end of the new film 15 is pulled out.
Numeral 18 denotes ultrasonic sensors which are disposed along the transport paths of the films 12 and 15 in order to detect the tail ends of the taken-out films 12 and 15. Numerals 20 and 21 denote a pair of opposing heaters which are adapted to separate and approach each other. When the ultrasonic sensor 18 detects the tail end of the old film 12, an unillustrated controller causes the heaters 20 and 21 to approach each other. The heaters 20 and 21 nip the old film 12 in the vicinity of the tail end thereof and the leading end of the new film 15, and heat them, thereby fusing and joining them at a joining point a, as shown in FIG. 2. With this operation, the old film 12 and the new film 15 are joined with each other. Numeral 12a denotes a residual flap of the old film 12 which is formed on the rear side of the joining point a.
However, when the old film 12 and the new film 15 are joined with each other in the conventional film joining apparatus, the controller starts the movement of the heaters 20 and 21 at the time when the tail end of the old film 12 passes by the ultrasonic sensor 18.
Since the amount of the old film 12 taken out from the old roll 11 varies depending on the packing pattern in which packaging containers are stacked, it is difficult to position the tail end of the old film 12 between the heaters 20 and 21 for fusion. Accordingly, a residual flap 12a of the old film 12 is formed on the rear side of the joining point
As a result, when the new film 15 is taken out from the new roll 14 without removing the residual flap 12a, a machine in a succeeding stage will not operate properly. Therefore, an operation for stopping the machine and removing the residual flap 12a must be performed before the residual flap 12a enters the machine in the succeeding stage.
An object of the present invention is to solve the problems of the conventional film joining apparatus and to provide a film joining apparatus which prevents a residual flap from being formed on the rear side of a joining point when film of an old roll and film of a new roll are joined, thereby eliminating the necessity of stopping a machine in a succeeding stage.